This invention relates to a system for simultaneously preheating at least one ladle to a relatively high temperature and curing another ladle at a lower temperature, wherein an open flame is directed into the ladles being preheated and the exhaust gases from the ladles being preheated are directed to the ladle being cured.
In the ferrous and nonferrous molten metals industries, ladles and similar metal receivers receive a charge of hot molten metal and transport the metal to a remote location for pouring the metal into a mold, or into a casting machine, etc. The receivers usually are lined with refractory material such as brick, and it is desirable to preheat the receiver before the hot molten metal is poured into the receiver in order to avoid interface solidification of the hot metal upon contact between the metal and a relatively cool interior surface of the receiver, and also to avoid thermal shock to the refractory liner of a relatively cool receiver, thus avoiding deterioration of the liner. When preheating ladles for the receipt of molten metal, it is desirable to preheat the ladles to temperatures as high as about 2400.degree. F. when the ladles are to receive molten steel or other molten ferrous materials. By preheating the ladle or other receiving chamber before pouring the metal in the ladle, significant heat loss from the molten metal to the ladle is avoided as the metal is transported in the ladle from the furnace to the pouring position.
The prior art procedures for preheating ladles and other molten metal receivers prior to charging the ladles with molten metal included directing an open, natural gas flame into the open chamber of the ladle. This open flame heating method permitted the hot combustion gases generated by the open flame to escape from within the ladle chamber to the surrounding atmosphere, thereby wasting heat energy.
Recently, a more economical system has been developed for preheating ladles, whereby a lid with a soft ceramic fiber face is applied to the rim of the ladle to be preheated to form a seal at the rim of the ladle, an open gas flame is projected from the lid into the ladle, and the exhaust gases are directed from the ladle back through the lid and through a heat exchanger which preheats the oncoming combustion air. This type of system is disclosed in U.S. Pat. No. 4,229,211 issued Oct. 21, 1980.
When a ladle has been rebuilt as by replacing the refractory brick at the interior surface of the ladle, before the ladle can be used it is necessary to dry or "cure" the ladle by slowly heating the interior of the ladle. The temperature of the refractory must be raised slowly in order to avoid cracking of the refractory during the drying procedure. Preferably, the temperature of the flame or other heat source within a ladle which is being dried should start at first from about 200.degree. F. and be raised slowly up to a temperature in excess of 1000.degree. F. Again, a prior art procedure for drying or curing ladles has been to direct an open gas flame into the ladle; however, this prior art procedure also is not economical in that the hot gases of combustion are lost to the atmosphere and it is difficult to control the temperature of the refractory surface within the ladle.
In a metal casting plant it is not uncommon to preheat several ladles to high temperatures while at the same time one or more other ladles which have been rebricked are being dried and further cured at lower temperatures.